[[servlet-authorization-filtersecurityinterceptor]]
= Authorize HttpServletRequest with FilterSecurityInterceptor
:figures: servlet/authorization

This section builds on xref:servlet/architecture.adoc#servlet-architecture[Servlet Architecture and Implementation] by digging deeper into how xref:servlet/authorization/index.adoc#servlet-authorization[authorization] works within Servlet based applications.

The {security-api-url}org/springframework/security/web/access/intercept/FilterSecurityInterceptor.html[`FilterSecurityInterceptor`] provides xref:servlet/authorization/index.adoc#servlet-authorization[authorization] for ``HttpServletRequest``s.
It is inserted into the xref:servlet/architecture.adoc#servlet-filterchainproxy[FilterChainProxy] as one of the xref:servlet/architecture.adoc#servlet-security-filters[Security Filters].

.Authorize HttpServletRequest
image::{figures}/filtersecurityinterceptor.png[]

* image:{icondir}/number_1.png[] First, the `FilterSecurityInterceptor` obtains an  xref:servlet/authentication/architecture.adoc#servlet-authentication-authentication[Authentication] from the xref:servlet/authentication/architecture.adoc#servlet-authentication-securitycontextholder[SecurityContextHolder].
* image:{icondir}/number_2.png[] Second, `FilterSecurityInterceptor` creates a {security-api-url}org/springframework/security/web/FilterInvocation.html[`FilterInvocation`] from the `HttpServletRequest`, `HttpServletResponse`, and `FilterChain` that are passed into the `FilterSecurityInterceptor`.
// FIXME: link to FilterInvocation
* image:{icondir}/number_3.png[] Next, it passes the `FilterInvocation` to `SecurityMetadataSource` to get the ``ConfigAttribute``s.
* image:{icondir}/number_4.png[] Finally, it passes the `Authentication`, `FilterInvocation`, and ``ConfigAttribute``s to the `AccessDecisionManager`.
** image:{icondir}/number_5.png[] If authorization is denied, an `AccessDeniedException` is thrown.
In this case the xref:servlet/architecture.adoc#servlet-exceptiontranslationfilter[`ExceptionTranslationFilter`] handles the `AccessDeniedException`.
** image:{icondir}/number_6.png[] If access is granted, `FilterSecurityInterceptor` continues with the xref:servlet/architecture.adoc#servlet-filters-review[FilterChain] which allows the application to process normally.

// configuration (xml/java)

By default, Spring Security's authorization will require all requests to be authenticated.
The explicit configuration looks like:

.Every Request Must be Authenticated
====
.Java
[source,java,role="primary"]
----
protected void configure(HttpSecurity http) throws Exception {
	http
		// ...
		.authorizeRequests(authorize -> authorize
			.anyRequest().authenticated()
		);
}
----

.XML
[source,xml,role="secondary"]
----
<http>
	<!-- ... -->
	<intercept-url pattern="/**" access="authenticated"/>
</http>
----

.Kotlin
[source,kotlin,role="secondary"]
----
fun configure(http: HttpSecurity) {
    http {
        // ...
        authorizeRequests {
            authorize(anyRequest, authenticated)
        }
    }
}
----
====

We can configure Spring Security to have different rules by adding more rules in order of precedence.

.Authorize Requests
====
.Java
[source,java,role="primary"]
----
protected void configure(HttpSecurity http) throws Exception {
	http
		// ...
		.authorizeRequests(authorize -> authorize                                  // <1>
			.mvcMatchers("/resources/**", "/signup", "/about").permitAll()         // <2>
			.mvcMatchers("/admin/**").hasRole("ADMIN")                             // <3>
			.mvcMatchers("/db/**").access("hasRole('ADMIN') and hasRole('DBA')")   // <4>
			.anyRequest().denyAll()                                                // <5>
		);
}
----

.XML
[source,xml,role="secondary"]
----
<http> <!--1-->
	<!-- ... -->
	<!--2-->
	<intercept-url pattern="/resources/**" access="permitAll"/>
	<intercept-url pattern="/signup" access="permitAll"/>
	<intercept-url pattern="/about" access="permitAll"/>

	<intercept-url pattern="/admin/**" access="hasRole('ADMIN')"/> <!--3-->
	<intercept-url pattern="/db/**" access="hasRole('ADMIN') and hasRole('DBA')"/> <!--4-->
	<intercept-url pattern="/**" access="denyAll"/> <!--5-->
</http>
----

.Kotlin
[source,kotlin,role="secondary"]
----
fun configure(http: HttpSecurity) {
   http {
        authorizeRequests { // <1>
            authorize("/resources/**", permitAll) // <2>
            authorize("/signup", permitAll)
            authorize("/about", permitAll)

            authorize("/admin/**", hasRole("ADMIN")) // <3>
            authorize("/db/**", "hasRole('ADMIN') and hasRole('DBA')") // <4>
            authorize(anyRequest, denyAll) // <5>
        }
    }
}
----
====
<1> There are multiple authorization rules specified.
Each rule is considered in the order they were declared.
<2> We specified multiple URL patterns that any user can access.
Specifically, any user can access a request if the URL starts with "/resources/", equals "/signup", or equals "/about".
<3> Any URL that starts with "/admin/" will be restricted to users who have the role "ROLE_ADMIN".
You will notice that since we are invoking the `hasRole` method we do not need to specify the "ROLE_" prefix.
<4> Any URL that starts with "/db/" requires the user to have both "ROLE_ADMIN" and "ROLE_DBA".
You will notice that since we are using the `hasRole` expression we do not need to specify the "ROLE_" prefix.
<5> Any URL that has not already been matched on is denied access.
This is a good strategy if you do not want to accidentally forget to update your authorization rules.